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Physics

Sound Intensity

Average sound intensity is acoustic power crossing an area divided by that area.

I = \frac{P}{A}

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Source & review

Difficulty

Intermediate

Read time

5 min

Prerequisites

Basic algebra, consistent units, and the stated model assumptions

Review statusNeeds review

Source

OpenStax, College Physics 2e, §17.3 (Paul Peter Urone and Roger Hinrichs)

OpenFormulaGraph equation reference; FormuLab adaptation details and license are provided below.

Adapted from OpenFormulaGraph, under CC BY 4.0.

FormuLab adapted wording, notation, applicability conditions and topic placement, and expanded the numerical check into a worked example.

Definition

Understanding the core concept

Average sound intensity is acoustic power crossing an area divided by that area. The area should be perpendicular to the energy flow, and a nonuniform field requires an area average.

Variables & Units

Understanding each component

Symbol	Meaning	Units
$I$	Sound Intensity	$W/ m^{2}$
$P$	Power	$W$
$A$	Area	$m^{2}$

Real-World Applications

Where this formula is used in practice

Acoustic power

Relate transported sound power to area.

Sound fields

Compare average intensities over perpendicular areas.

Worked Example

Step-by-step calculation with real numbers

Problem

A sound wave carries 0.0200 W through a perpendicular area of 4.00 m². Find its average intensity.

Given

P = 0.02 W

A = 4 m^{2}

Solution

I = \frac{P}{A}

I = \frac{( 0.02 W )}{( 4 m ^{2} )}

I = 0.005 W/ m^{2}

Final Answer

I = 0.005 W/ m^{2}

Formula Guide

Info

DifficultyIntermediate

Read Time5 min

PrerequisitesBasic algebra, consistent units, and the stated model assumptions

Tools

Source & review

StatusNeeds review

Last reviewedPending

Source

OpenStax, College Physics 2e, §17.3 (Paul Peter Urone and Roger Hinrichs)

OpenFormulaGraph equation reference; FormuLab adaptation details and license are provided below.

Adapted from OpenFormulaGraph, under CC BY 4.0.

FormuLab adapted wording, notation, applicability conditions and topic placement, and expanded the numerical check into a worked example.

Assumptions

• Use acoustic power crossing the stated area, rather than total source power unless all of it crosses that area.
• Use a uniform intensity or interpret the quotient as an area average.

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Sound Intensity

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